This invention relates to a multi-purpose electronic apparatus and more particularly an electronic apparatus with calculator functions and electronically tuning radio receiver functions and, if desirable, timekeeper functions.
It is an object of the present invention to provide electronics which enable an integral and efficient combination of an electronic calculator and an electronically tuning radio receiver and/or an electronic timekeeper. More particularly, the object of the present invention is achieved by a microprocessor semiconductor LSI chip.
The functions of an electronic calculator are generally focused on the conventional four-rule calculations and executed in an interrupted manner of key actuations.fwdarw.arithmetic operations.fwdarw.displays. A display mode occupies a substantial amount of time while the calculator is in use, whereas a calculation mode is available for only a very limited length of time per day, for example. A pause period for the control circuitry of the calculator is therefore relatively very long. It is desirable to take advantage of operability of the control circuitry of the calculator for other than continuous calculator use. For example, provided that the calculation mode is interrrupted at the time when such interruption has no influence on arithmetic operations, for example, a display mode after the completion of calculations, it would be possible to realize real-time multiplexing of the control circuitry.
A conventional radio receiver, on the other hand, is tunable by varying the capacitance or inductance of a tuning circuit, for example, by a mechanical device. The conventional radio receiver could be expected only to serve as a special-purpose device. In recent years, a new tuning method, a so-called electronically designed digital tuning method has been developed to exploit new fields of the radio receiver. The digital tuning method replaces the conventional tuning circuit by a phase locked loop ("PLL") which essentially consists of a variable (programmable) divider, a phase detector, a low pass filter and a reference frequency oscillator. The reception frequency of the PLL tuning circuit is determined by input data applied to the programmable divider as digital codes which makes it possible to put digital tuning into practical use.
In addition, recently developed electronic timekeepers have been designed to operate in a digital fashion.